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authorgdisirio <gdisirio@35acf78f-673a-0410-8e92-d51de3d6d3f4>2011-12-29 18:03:49 +0000
committergdisirio <gdisirio@35acf78f-673a-0410-8e92-d51de3d6d3f4>2011-12-29 18:03:49 +0000
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I2C API proposal.
git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@3684 35acf78f-673a-0410-8e92-d51de3d6d3f4
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# Backlighting

Many keyboards support backlit keys by way of individual LEDs placed through or underneath the keyswitches. This feature is distinct from both the [RGB underglow](feature_rgblight.md) and [RGB matrix](feature_rgb_matrix.md) features as it usually allows for only a single colour per switch, though you can obviously install multiple different single coloured LEDs on a keyboard.

QMK is able to control the brightness of these LEDs by switching them on and off rapidly in a certain ratio, a technique known as *Pulse Width Modulation*, or PWM. By altering the duty cycle of the PWM signal, it creates the illusion of dimming.

The MCU can only supply so much current to its GPIO pins. Instead of powering the backlight directly from the MCU, the backlight pin is connected to a transistor or MOSFET that switches the power to the LEDs.

## Feature Configuration

Most keyboards have backlighting enabled by default if they support it, but if it is not working for you, check that your `rules.mk` includes the following:

```makefile
BACKLIGHT_ENABLE = yes
```

## Keycodes
Once enabled the following keycodes below can be used to change the backlight level.

|Key      |Description                               |
|---------|------------------------------------------|
|`BL_TOGG`|Turn the backlight on or off              |
|`BL_STEP`|Cycle through backlight levels            |
|`BL_ON`  |Set the backlight to max brightness       |
|`BL_OFF` |Turn the backlight off                    |
|`BL_INC` |Increase the backlight level              |
|`BL_DEC` |Decrease the backlight level              |
|`BL_BRTG`|Toggle backlight breathing                |

## Backlight Functions

|Function  |Description                                                |
|----------|-----------------------------------------------------------|
|`backlight_toggle()`    |Turn the backlight on or off                 |
|`backlight_enable()`    |Turn the backlight on                        |
|`backlight_disable()`   |Turn the backlight off                       |
|`backlight_step()`      |Cycle through backlight levels               |
|`backlight_increase()`  |Increase the backlight level                 |
|`backlight_decrease()`  |Decrease the backlight level                 |
|`backlight_level(x)`    |Sets the backlight level to specified level  |